I am using phpBB that Scott helped setup for me. Granted it is not the best system, but forums take a while to get going. If I recall, Scott used a different system when Lateral-g first got started? You may consider using the free forums to start and if they take off and get active then upgrade?
phpBB doesn't have alot of the tools and tricks that Vbulletin does, but it does the job.
You can see what my phpBB forum looks like
www.college-investor.com
Good Luck.
Tim